Title of Invention

"DIRECT INJECTION INTERNAL COMBUSTION ENGINE"

Abstract

In the case of a direct-injection internal combustion engine, in particular a spark-ignition engine, with layered lean-burn operation and internal exhaust gas recirculation, NOx-reducing exhaust-gas aftertreatment is provided by means of an NOx storage catalytic converter. To achieve the highest possible exhaust gas recirculation rates in combination with the lowest possible HC and NOx emissions, tumbling flow is provided for the fresh gases flowing in, which if appropriate may contain recirculated exhaust gas from external exhaust gas recirculation, so that the turbulence axis of the fresh gases flowing in runs substantially transversely with respect to the movement of the piston. This results in emission-reducing optimum mixing in the cylinder interior during layered lean-burn mode.

Full Text

The present invention relates to direct-injection internal combustion engine. EP 0 560 991 B and EP 0 580 389 B have disclosed devices for reducing the levels of NOx in lean-burn internal combustion engines. The principle of these arrangements is that of storing the NOx formed in particular during lean-burn operation of the internal combustion engine in an NOx storage catalytic converter and releasing the stored NOx with simultaneous reduction by briefly operating the internal combustion engine in rich-burn mode. This NOx conversion is also suitable in particular for direct injection internal combustion engines. With the NOx conversion describedit is already possible to achieve relatively high conversion rates, and exhaust gas recirculation can be used in combination with the NOx storage catalytic converter in particular to avoid raw NOx emissions. The raw NOx emissions are in priflciple considerably reduced by the exhaust gas recirculation. This measure is particularly important in lean-burn, direct-injection spark-ignition engines with NOx-reducing exhaust-gas aftertreatment system, in particular NOx storage catalytic converters, since the lean-burn conversion can result in very high raw NOx emissions, as occur in particular in homogeneous lean-burn operation with lambda = 1.1 to 1.4 or in layered lean-burn operation at lambda = 1.6 to 4, even when using NOx storage catalytic converters, possibly as a result of diffusion being inhibited at the storage catalytic converter surface. Furthermore, the recirculated exhaust gas leads to a drag in combustion, which firstly also has the effect of reducing the levels of NOx on account of the reduced combustion temperature, and secondly improves fuel consumption, since the center of gravity of fuel conversion, which typically in direct-injection spark-ignition engines is too early in the cycle when using layered lean-burn operation, is shifted toward the optimum position. Moreover, given suitable metering, the hot, recirculated exhaust gas may also lead to combustion being stabilized in the layered lean-burn operation, since the temperature, which is increased by the exhaust gas recirculation, assists the formation of the mixture, which in principle, on account of the fact that injection is late in this operating mode, has to take place within a very short time scale. However, the proportion of recirculated exhaust gas in the combustion chamber must also not be selected to be excessively high, so that there is sufficient fresh gas available for combustion of the fuel. If the exhaust gas recirculation rates are too high, combustion is incomplete, so that consumption and HC/CO emissions increase again and the smoothness of the engine decreases. In the case of external exhaust gas recirculation (tapping off the exhaust gas downstream of the combustion chamber, in particular at the exhaust manifold, and returning it to the induction side of the internal combustion engine), which is usually carried out, homogeneous distribution of the exhaust gas to the individual cylinders can only be achieved with a high design outlay. Moreover, the exhaust gas recirculation rate in dynamic operation which is present in particular in an internal combustion engine can only be adjusted and matched to set stipulations with difficulty, on account of the time delay produced by the exhaust gas recirculation line and the induction duct volume, as well as the fluctuating pressure conditions on the induction and exhaust sides. Accordingly, the exhaust gas recirculation rate may differ considerably between the individual cylinders, and it is impossible to reliably avoid the possibility of undesirable minimum levels riot being achieved and of undesirable maximum levels being exceeded. As an alterncitive or in addition to external exhaust gas recirculation, internal exhaust gas recirculation is known, in which, as a result of the intake and exhaust times being adjusted with respect to one another, in particular by adjusting the intake camshaft toward "early", it becomes possible for a residual gas content to remain in the cylinder. The advantage of this method, in addition to accurate cylinder-individual me;tering, is that the residual gas is already involved in the next combustion operation, and the dead times described above and also the considerable deviations from a desired value are largely eliminated. On account of the higher temperature of the internally recirculated exhaust gas, the; influence on mixture formation is also more significant and can be utilized in a more controlled way. The above-described advantages of internal exhaust gas recirculation are utilized in the first commercially available direct-injection spark-ignition engines which, in addition to external exhaust gas recirculation, also have internal exhaust gas recirculation with intake camshaft adjustment and exhaust-gas cleaning by means of an NOx storage catalytic converter. In these internal combustion engines, a swirling concept for moving the charge, in which a rotary movement is imparted to the gases which have been sucked in in the cylinder, with the axis of rotation running approximately parallel to the movement of the pistons/the axis of the cylinders, is used to from the mix. Stationary air turbulence is generated in the combustion chamber into which the fuel jet is injected and guided to the spark plug, Combustion methods of this type, in combination with an NOx storage catalytic converter, already achieves very low levels of NOx emissions, According to the present invention there is provided a direct-injection internal combustion engine, having NOx-reducing exhaust -gas aftertreatment, internal exhaust gas recirculation, layered. lean-burn operation, and turbulence in the fresh gas flowing in, wherein the turbulence has a turbulence axis which runs predominantly transversely with respect to the piston movement characterized in that the turbulence is generated by a tumble plate in the induction duct. The subclaims describes further measures by means of which, individually and in combination, it is possible to achieve particularly favorable emissions values. According to the invention, particularly, low emissions of pollutants, in particular NOx, is achieved by a special combination of "individual exhaust-injection internal combustion engines can now satisfy the most stringent exhaust gas standards, such as for example D4. This is made possible, in a direct-injection combustion engine, by internal exhaust gas recirculation (EGR), in particular in combination with external EGR, NOx-reducing exhaust - gas aftertreatment and turbulent motion of the (fresh) gases flowing in, which runs predominantly transversely with respect to the movement of the pistons. In this context, it is preferably to use a tumbling motion of the gases flowing in, which is advantageously generated by a tumble plate in the induction duct. With a tumbling motion of this type, the gases flowing in roll into the cylinder interior, the rolling movement taking place about an axis which is transverse with respect to the movement of the pistons. A tumble plate is preferably used in combination with, where necessary, switching from flow with tumbling turbulence to ordinary filling of the cylinder chamber, as is customary, for example, in the case of lambda-1 operation (regeneration of the storage catalytic converter, high engine load). Combining internal EGR with external EGR allows the exhaust recirculation rate to be increased further, so that the lowest possible excess of oxygen can be used. In this case, it is also possible for the external EGR to be cooled by means of an exhaust gas recirculation cooler, so that the combustion chamber temperature does not rise to be excessively high. The external EGR is usually controlled by means of a valve. According to the invention, the turbulence axis preferably lies in a range of ± 15° with respect to the piston movement; the lowest NOx emissions are achieved in this range. In particular, according to the invention, an NOx storage catalytic converter which stores the nitrogen oxides in the raw exhaust emissions for a number of seconds (usually up to approx. 2 min), for example in the form of barium nitrate, and is regenerated by reduction during operation with lambda With the present invention, it is particularly advantageously possible to use an NOx sensor after the NOx-reducing step of exhaust-gas aftertreatment, in particular in combination with a storage catalytic converter. In previous operating systems without the tumbling motion, it was easy for NOx to break through, and for these events to be incorrectly assessed by the NOx sensor as meaning that the storage catalytic converter needed to be regenerated, so that regeneration, which increases fuel consumption, took place too frequently. The NOx peaks were only avoided by the use of the tumbling motion, so that, according to the invention, the NOx sensor downstream of the storage catalytic converter for the first time signals reliable storage rates and therefore filling levels of the NOx storage catalytic converter. According to the invention, it has been found that, to optimally reduce the levels of NOx, it is necessary to ensure that mixing of the recirculated exhaust gas with fresh air is optimized, since only in this way can the oxygen molecules involved in the formation of NOx be partially replaced by inert gas (exhaust gas) throughout the entire combustion chamber. The- formation of rapidly burning local zones with a high oxygen content, which make a disproportionately large contribution to the formation of NOx, is avoided in accordance with the invention. This particular feature is important especially in the case of direct-injection spark-ignition engines, in orde?r for it to be possible for the potential of internal exhaust gas recirculation to be utilized as completely as possible in such engines. The invention is described in more detail with reference to an exemplary embodiment and figures, in which: Figure 1 shows a combustion sequence according to the prior art (swirl concept); Figure 2 shows the combustion sequence according to the invention (tumbling concept); Figure 3 shows a graph illustrating the two concepts; and Figure 4 shows an overall illustration of the concept according to the invention. Tests carried out in accordance with the invention have shown that the mixing of the fresh air 6 with the exhaust gas 3 from the internal exhaust gas recirculation, which has remained in the combustion chamber 1 (Fig. la, piston 2 is at the top, and simultaneously opened intakes and exhaust valves (Fig. 4) result in exhaust gas 3 remaining in the combustion chamber 1) is less than optimum with swirling turbulence 7 (turbulence axis oriented substantially in the same direction as the movement of the piston/axis of the cylinder) . The residual gas 3 from the internal EGR remains in the vicinity of the piston base during the induction and compression strokes (Fig. Ib/c) on account of the action of the swirling flow 7 in the vicinity of the piston base, and the fresh gas 3 which is suck inhomogeneous mixed zones 5 with fluctuating fresh air/residual gas ratios and is partially injected into virtually pure residual gas 3 (Fig. Ic) . During the conversion (ignited by spark plug 4) , therefore, residual gas contents of virtually 0% to virtually 100% may therefore occur in the flame front, and the approximately optimum residual gas content is only locally present in small areas of the combustion chamber 1, even though the overall residual gas content may very well match the set stipulations. In the zones where there is little or no residual gas, the fuel fraction burns rapidly and at; high temperatures, so that here there is scarcely any significant reduction in the levels of NOx. In the zones with a very high residual gas content, the fuel conversion fails, so that the exhaust gas, in addition to the fact that the levels of NOx are only slightly reduced, may also have increased HC emissions and the work formed may be reduced. In addition, consumption may increase and smoothness of the engine may deteriorate, leading to a failure in the desired stipulation of the exhaust gas recirculation rate, so that the potential to reduce NOx is restricted even further. In principle, even with the swirling motion it is possible to take account of this layered arrangement, for example by designing the piston base in such a way that either turbulence is effected again during compression or the injected jet passes into a region which is homogeneous as possible, but according to the invention is has been found that better, i.e. lower NOx emission levels can be achieved by switching to tumbling turbulence, in particular in combination with a NOx sensor. Depending on the exhaust concept, the higher levels of HC and NOx emissions formed can be reduced in particular by selective catalytic reduction, i.e. reciprocal reduction and oxidation, so that overall it is once again possible to achieve relatively low exhaust emissions levels, but this is to the detriment of the consumption and the smoothness of the internal combustion engine. As illustrated in Fig. 2, according to the invention, internal exhaust gas recirculation (as in Fig. 1) also takes place by adjustment of the intake camshaft, but in this case with a tumbling charge motion concept 17 (the axis of rotation of the gas sucked in is substantially transverse with respect to the movement of the piston) . At the start of the induction cycle (Fig. 2a, piston 12 at the top), there is, as in Fig. la, a high residual gas content 13 in the cylinder chamber 11. Compared to the prior art, however, the method according to the invention has the advantage that the subsequent charge motion (Fig. 2b) leads to intensive mixing of the residual exhaust-gas content 13 with the fresh gas 16 which is sucked in (if appropriate enriched with exhaust gas from the external exhaust gas recirculation) . As can be seen from Fig. 2c, the fuel 18 which is injected therefore enters a gas mixture in which the local residual gas content deviates only slightly from the mean (overall) residual exhaust gas content (substantially homogeneous mix 15). This prevents the flame (ignited via spark plug 14) from being extinguished as a result of excessively high local residual exhaust gas levels and, at the same time leads to idecil reduction in the levels of NOx in the raw exhaust gas without the HC emissions being adversely affected and with high smoothness and low consumption. This allows high set stipulations to be put in place for the residual exhaust gas content in the fresh gas.. This is illustrated in Fig. 3, from which the lower spread of the local deviation of the residual exhaust gas content in the combustion chamber can be seen. The overall residual exhaust gas content in the combustion chamber is denoted by 30. The undesired range of excessively low NOx reduction (too much O2) is denoted by 31, while the undesired range of insufficient fuel conversion (formation of CO/EC, too much exhaust gas) is denoted by 32. Curve 33 represents the tumbling concept, curve 34 reveals a higher inhomogeneity for the swirling concept. According to the invention, even with a high exhaust gas recirculation rate, the maximum permissible residual gas content is as far as possible not locally exceeded in the tumbling concept. The overall concept shown in Fig. 4 represents part of the internal combustion engine 50, which has a fresh-air intake duct 51, through which, in layered charge operation, the fresh gases flowing in are passed into the combustion chamber 11, together with exhaust gases which are recirculated via an exhaust gas recirculation line 68, in a tumbling flow 17 imparted by a tumble plate 52. The recirculated exhaust gases are controlled according to operating conditions by the engine management system 66 using a valve 67 and, moreover, are cooled by means of a EGR cooler 69. The compression stroke as in Fig. 2c, in which the fuel 18 is being injected, is illustrated. The internal combustion engine 50 also has an intake camshaft 55 and an exhaust camshaft 56, which actuates the intake valve 53 and exhaust valve 59 via drag levers 54 and 57 . These valves are accommodated in the cylinder head 58. The filling of the combustion chamber 11 with exhaust gas 13 (Fig. 2a) is achieved by opening the valves 53 and 59. The valves 53 and 59 are closed during the compression operation. After combustion has taken place, the piston 12 moves downward again, and the exhaust valves 59 are opened, so that the exhaust gases 60 flow into the exhaust manifold 70. In the process, they flow past a lambda sensor 61, which is designed as a wide-band lambda sensor and is used to determine the lambda from rich to lean. Then, the exhaust gases 60 flow through a primary catalytic converter 62, which is designed as a three-way catalytic converter. In the process, CO and HC can already be converted, using the oxygen which is present, into CO2 and H20, and moreover NO is oxidized to form N02. Downstream of the primary catalytic converter 62, there is a temperature sensor 63, which is used for monitoring (OBD) of the catalytic converter 62. The exhaust gases flow onward into an NOx storage catalytic converter 64, which in particular absorbs the nitrogen oxides. As the filling level increases, there is an increasing NOx slippage through the NOx storage catalytic converter 64, and this is recorded by the NOx sensor 65. This signal is evaluated by the engine management system 66 in such a way that, when a defined level is exceeded, the NOx storage catalytic converter 64 is to be regenerated. This takes place by means of brief (up to approx. 5 seconds) rich-burn operation of the internal combustion engine 50, during which time H2, CO and HC pass into the NOx storage catalytic converter 64 and react with the NOx released under these operating conditions to form N2, H20 and CO. Then, the engine is switched back to lean-burn mode. The regeneration and also high-load operation are advantageously carried out under homogeneous operating conditions of the internal combustion engine 50, in which the flow-contact part 71 of the tumble plate 52 is flattened (placed onto the wall of the intake duct 51), so that the fresh gases flow past the tumble plate 52, and as a. result there is no tumbling turbulence imparted in the combustion chamber 11. In the case of a direct-injection internal combustion engine, in particular a spark-ignition engine, with layered lean-burn operation and internal exhaust gas recirculation, NOx-reducing exhaust gas aftertreatment is provided by means of an NOx storage catalytic converter. To achieve the highest possible exhaust gas recirculation rates in combination with the lowest possible HC and NOx emissions levels, tumbling flow is provided for the fresh gases flowing in, which if appropriate may contain recirculated exhaust gas from external exhaust gas recirculation, in such a way that the turbulence axis of the fresh gases flowing in runs substantially transversely with respect to the movement of the piston. This results in emission-reducing optimum mixing in the cylinder interior during layered lean-burn mode. WE CLAIM: 1. Direct-injection internal combustion engine, having NOx-reducing exhaust -gas aftertreatment, internal exhaust gas recirculation,' layered lean-burn operation, and turbulence in the fresh gas flowing in, wherein the turbulence has a turbulence axis which runs predominantly transversely with respect to the piston movement characterized in that the turbulence is generated by a tumble plate in the induction duct. 2. Internal combustion engine as claimed in claim 1, wherein the turbulence is a tumbling motion. 3. Internal combustion engine as claimed in claim 1 or claim 2, wherein the turbulence is generated by a tumble plate in the induction duct. 4. Internal combustion engine as claimed in any one of the preceding claims, wherein it is a spark-ignition engine. 5. Internal combustion engine as claimed in any one of the preceding claims, wherein it additionally has external exhaust gas recirculation. 6. Internal combustion engine as claimed in' claim 5, wherein the external exhaust gas recirculation is cooled and/or provided with a control valve. 7. Internal combustion engine as claimed in any one of preceding claims, wherein the turbulence axis lies in the range from 75° to 105° with respect to the piston movement. 8. Internal combustion engine as claimed in any one of preceding claims, wherein the exhaust-gas aftertreatment takes place by means of an NOx storage catalytic converter. 9. Internal combustion engine as claimed in any one of preceding claims, wherein the exhaust -gas aftertreatment is controlled by an NOx sensor. 10. Internal combustion engine as claimed in any one of preceding claims, wherein the internal exhaust gas recirculation takes place by adjusting the intake-valve opening times towards early. 11. Direct-injection internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

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in-pct-2002-00436-del-abstract.pdf

in-pct-2002-00436-del-claims.pdf

in-pct-2002-00436-del-correspondence-others.pdf

in-pct-2002-00436-del-correspondence-po.pdf

in-pct-2002-00436-del-description (complete).pdf

in-pct-2002-00436-del-drawings.pdf

in-pct-2002-00436-del-form-1.pdf

in-pct-2002-00436-del-form-19.pdf

in-pct-2002-00436-del-form-2.pdf

in-pct-2002-00436-del-form-3.pdf

in-pct-2002-00436-del-form-5.pdf

in-pct-2002-00436-del-gpa.pdf

in-pct-2002-00436-del-pct-210.pdf

in-pct-2002-00436-del-pct-304.pdf